Previously microelectronic structures employed aluminum alloys with silicon dioxide dielectrics for interconnect systems in integrated circuits. Numerous cleaning compositions were developed and available for satisfactorily cleaning post etch residue from such microelectronic substrates in the back end of the line (BEOL) processing. However, with the need for smaller and smaller geometries to meet the need for increased speed and integration density these aluminum/silicon dioxide interconnect systems have been shown to be inadequate. Consequently, copper-dual damascene structures with low-k dielectrics have been developed and are replacing the aluminum/silicon dioxide interconnects.
However, these Cu-dual damascene interconnect structures have presented a whole new set of parameters and problems for BEOL cleaning steps. For example, when employing a very diluted aqueous HF based acidic solution to produce a post-etch Cu-dual damascene structure on a silicon substrate, any CuOx and Cu(OH)2 films or residues on the surface are dissolved in the acidic fluoride environment and thus produce large amounts of copper (Cu2+) ions in the solution according the following equation.Cu(OH)2+2HFCu2++2F−+2H2O
As a result of copper vias in the structure, electrically connected through a P—N junction fabricated in the silicon substrate, there can occur significant undesirable redeposition (also called copper extrusion) where the copper vias are connected to the electron rich N doped regions by an electrochemical reaction as represented by the following reduction reaction equation.Cu2++2e−→CuSuch cathodic redeposition of copper is highly undesirable and results in large copper features that extend out from the specific vias which would result in defects during subsequent processing steps. It is also expected that Cu redeposition will occur in other cases where highly charged cathode surfaces are exposed to cleaning solutions where Cu2+ is present as a result of the cleaning process
It is therefore highly desirable to be able to provide an acidic compositions for use in copper oxide etch removal and wherein that composition prevents or substantially eliminates copper redeposition on a Cu-dual damascene microelectronic structure.
With the advent of the use of copper interconnects passivation of such interconnect has also changed. Instead of passivating the copper with dielectrics such as with SiN or SiCN dielectrics and addressing the resulting problems of such passivation, the industry has begun to avoid those problems with the use of self-aligned metal caps that produce improved electromagnetic and stress lifetimes by the use of, for example CoWP metal capping layers for the copper interconnects. However, it is important that the durability of the capping layer be maintained during etch and stripping processes. Therefore, in a further embodiment of the present invention it is desirable that the acidic composition for use in the copper oxide etch removal that prevents or substantially eliminates copper redeposition on a Cu-dual damascene microelectronic structure also be able to maintain the durability of the metal capping layer during etch and stripping processes.